savory



Aug.11,1959 bB. sAVb Y l l 8 9 coNTRoL APPARATUS- d m 29l 1957 2 sheets-Sheet Invenfor Dnvid B. sqVory His A+forney Augo 11, 1959 D. B. sAVoRY cONTROL APPARATUS 2 SheetSSheet 2 F1ea Apf1 29, 1957 Time His AH rney 1afof contro11ef arTanged so that it cyc1icany chargeS and dischargeS iI1 Tesponse to changes in f11e oscillatofy co1 dtion of the contToner,

The chafging and diSchafging action modifies the eect of the coil and vane aSSen1bly alSo foTIniI1g a part of the inpuf cifcuit and pTovides excellent StTaight1ine control thefewith.

By aSSociating a1 adinStable TeSisto1 vvith the condenS of, the pefiod for cycli11g the charging and diScharging acfion of the condenSef n1ay be vafied to accon1n1odato the neods of pafticu1af pfoceSSes vithiI1 coftain predeter Inined Hmits.

The invention fogethe1 With itS objects and advantages vvi11 be beSt undeTStood Ilpon fefefence to the specification set foTth be1ovv, particulaT1y when taken vvith the ofavvingS anneXed hereto in vvhich= Fignfe 1 iS a snbstantiany Schenlafio arfangen1ent of a oontroHer vvith an aSSociated elecfTic furnace;

Figure 2 iS a cifctlit diagraII1 of the inpfoved oSci11atof oontroner,

Figure 3 is a graph shovving the Telationship betvveen osciHatof grid voltage and vane position; and Figure 4 iS a graph illllStTating the effect on contro1 actioI1 defived thTongh the cyclic ChaTging and diSchafging of the condenSe1 fofn1ing a paft of the iIIlpfoved contro1 lef.

Referring 1i1St to Figufe 1, there iS Shown iI1 Schematic forIn a fuTnace 5 vvhich confainS an electfic heating Ilnit 5 adapted to be contToHed by the oscillatoI contTonef 7 Which SenSeS the tenlperatuTe within tho furnace thfough a detecfor in the forn1 of thernocouplo 8.

The therInocoUple is connected to a snitable n1i11ivo1t meter, paTt of Which iS Shown at 9, Which may be of the high reSiStance, perInanent nlagnet, n1oving ooil type, The Inillivolt oufput of the theTn1ocouple caUSes de11ec tion of the Inoving coil 11 fofn1ing a paft of the Inillivo1t- Ineter and aS the coi1 Inoves, it caffieS an aSSociated point of 12 across a sI1itable indicating scalo 13. Secufed to the pointer 12 near its outer end is a xnetallic vane 14 Which iS adapted to cooPerate vvith a paiI of spaced senSing coilS shovvn at 15 Inounted on a pivota1ly n1ounted set-point ad iusting arm 15,

T11e coil and vane asSen1bly Inay be of the type shovvI1 and descTibed in the afofSaid Miche1 patent ad com priseS a pair of Seriany connected, i1at, Spifally Wonnd pancake coiIS arranged side by sido vvith a Space betvveen oI1 a Suitable suppofting StTI1ct11Te, Tho coils afe thuS iI1 ductively Telated to each other such that the inSeTtion of the vane 14, vvhich Inay bo of any Suifable electricany con ducting nlaterial SI1ch aS coppef, vvi11 feduce the IIlutual inductance betvveen the coilS and alSo feduce fheir self inductane, This effect is IItilized to contro1 the action of the oS- ci11ator an1pliner 17 which iI1 tuTn vvill contro1 the action of a Telay 18 Which, as ShoWn in Figuro 1, Win contfo1 the action of heater o.

Positioning of tho set-pointef 15 along the scale 13 vvi11 enable the feInpefatufe of the fuTnace to be estab lished vvithi11 any pTedetern1ined liITlits and the actio1 of the coil and vane aSSeInbly, togethef With the oScillator afopH5er, vvill seTve to contro1 the tenlperatufe of the fnfnace at the setpoint of the control unit.

poinfer stop 19 iS Shovvn to prevent the vane 14 fTon1 going beyond the space betWeen the coil asSembly 15.

The action of the oScillator WiH be best underSfood 11poI1 Teference to FiguTe 2 vvherein there is shovvn a twin tfiodo 21 conlpTising an osoillating half 22 and a TePeatef of afIlplifief half 23. v ConSidering St the oSci1lator poTtion of tho tvvin friode, it iS Seen that it has a plate 24, a gTid 25 and a cathode 25, together vVith a SIlitable filan1eI1t 27 vvhich nlay be USed to heat both cathodes WithiI1 the tube,

The oScillatof 22 is SubStantiaHy sini1a1 to the osci1- lator shown in the afofeSaid Michel patent and its action vvi11 be descTibed but brief1y since fefefence to fhe te f vvi11 affoTd a conlp1eto descfiption of thiS type of osci1 latof contToner. v

ThnS, the oscillatof haS an output ci1c1it Which in cludes the Secondafy 28 of the 21.(. enefgiziI1g ffans foTITler, the prin1ary of vvhich is shovvn at 29. A1So in oluded in the output circuit of osci11atof 22 is a feSistof 31 acfoss vvhich a pfedetern1ined vafiablo voltago drop can be developed in fesponSo to changes i11 the osci11atofy conditioI of the oscillatof.

T11e anode 24 is alSo con1ected to the inpllt cifcuit of the oScinatof thTough a condenSef 32 andjnductof 33. The plafe iS connected to one end of the1nductof and the othef end of the indnctof iS connected thfough a gfid cifcuit condenSef 34 fo the grid 25 of tho osciHatof. (:o1- Ilected neaf tho I)1afe end of inductof 33 iS a 1ead ffon1 the Serially connected senSing coils 15 vvith the other end of the sensing coils connected by a Suitable lead to the cathode fetufn of the oScillatof, (frid leak fesiStof 35 is connected betvveen the gTid and cathode of tho osoi11atof 22 sllch that the oScinatof is Se1f-biasing, and a con denser 35 is connected across the n1ain poTtionS of induc tor 33 via the sensing coi1S 15 to foTm the pafalle1 foS onant ciTcuit of the oScillatof.

2S iS cleafly deScfibed in the afofeSaid Miche1 pafent, the poftion of fhe inductof 33 befvveen the plate and sensing coils actS as a tickler coil forregeneTative feed back and enables the oscillator to develop suStained os cillatioI1 aS Tequired. It iS to be noted that the inductof is pfovided With an axially adjustable iTon cofe lIlelT1bof 33o vVhich is provided to conlpenSate fof 1I1annfactufi11g foleTanceS in order to peTInit slight adinstlTlents i11 foe(1- back to allovv the pointef 12 to line up pTopefly With the setpoint at the stabiliZed opefating condition of the paf, ticulaf pfocess being contToned.

AS explained in the l/1ichel pate1t the senSing coils 15 function aS a degenefative feedback conpling Which sub Stantiany cance1s the fegenefative foedback when the vano 14 iS vvho11y Without the space betvveen the coi1S Such that a low leve1 oscinatofy condition is eStablished Which allowS Substantially IIlaXiITluIn cuffent i11 the output cif cuit of the oScinatof. 1efefTing to the pfoceSS shown in 1=ig11ro 1, this condition would pTevail when the hoatef iS fifst energized and during the time When the tompefa tuTe vvithin the furnace is being bfought up to the fequired Sef-poinf.

TO avail of the cufrent in fhe load ciTcuit of the oScil 1ator aS a Ineans of confroning the heatef 5, there iS pfovided tho aInplifier 23 Which haS a plate 37, grid 38 and cathode 39. The aInp1if1ef 23 is eneTgized ffon1 the oufce 29 thfough a tapped portion of secondary 28 and its outpot cifcnit includes the Winding 41 of felay 18. Bias on the grid of tho an1pHnef iS deTived froIn a fixed tap on secondary 28, togethef With the fesisto1 42 and the voltage drop acfoSS fesiStor31. A condenSof 43 is connected acfoss the felay Winding.

vvhen the curront in fhe output cifcuit of oScillatof 22 iS at a InaxiInllm, Whi ch cofTesponds to an initial oSci1 1atory condition of tho osci11ator, the voltage dTop across TeSisto1 31 is corTeSpondingly at a maximn. Since in the circuit ShoWn theXed tap in the gTid cifcuit of ampHHef 23 developS 30 vo1tS,^the TesiStor 31 iS Such that th the ITa(iInUIn cuffent of aboIlt five Inillian1pefes f1owing, itS vo1tage drop is abouf 32 vo1tS andJ is of opposite polarity to the HXed voltage derived ffom the tap on secondary 28. This Tesu1ts in abont 2 vo1tS on gTid 38 Which anovvS the an1p1ifier 23 to conduct and eneTgize felay vvinding 41.

ASsociated With Winding 41 afe a paif of Single-pole, double-throvvSWitches 43, 44, Which include the nxed contactS 45, 45, aod 47, 48, Tespectively. The svvifch 44 Inay be 11sed to cont o1 the he ate o difectly, in Whiob evoht fhe Inovable contact Wi11 o1ako with fixed contocf 48-to eflergizo the hoafer vvhioh could be connocted acfoS fhe terII1ihalS 49, 51.- ZXc fosS te n1inalS 49 and 52oou1d 

